Determination of Functional Failures

DOE-STD-1052-93

7.5.2

Determine the function(s) of each system and subsystem by reviewing plant

system descriptions, Final Safety Analysis Reports (FSARs), P&IDS, Technical

Safety Requirements (TSRs), operating procedures and instructions, abnormal

operating procedures, emergency operating procedures, and design basis

documentation. If functions, such as providing a vent or drain path, are

determined not to be important to the overall purpose of the system or

subsystem, then these functions may be omitted. Omission of specific functions

(or other assumptions) should be noted in the data package along with the

technical basis for the omission. System or subsystem function(s) should be

listed on a tabulation form.

7.5.3

When determining system and subsystem functions to analyze, the analyst

should consider that a system and subsystem typically perform a number of

auxiliary functions in addition to their primary function(s). The analyst should

carefully review the auxiliary functions of system and subsystem to identify

those functions that should be preserved. Auxiliary functions may include the

following:

Maintain pressure boundary integrity.

Provide indication required by technical safety requirements.

Automatically shut down components.

Provide input signals for local instrumentation.

Provide miniflow protection for pumps.

7.6

Determination of Functional Failures

This section describes a method for determining likely component failures that may

cause the loss of system or subsystem function(s). A functional failure exists when a

component ceases to provide a required function whether the function is active or

passive, evident or hidden. Some functional failures identified may be judged to be

implausible. Examples of implausible failures are those manufacturing defects that

escaped detection during installation and operational testing, the result of an

unexpected failure mechanism, or a failure that requires a rare or unexpected external

occurrence.

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